Isotope receiver for a calutron having an oil reservoir in its collection pocket



April 4, 1967 w.. A. BELL, JR, ETAL 3,

ISOTOPE RECEIVER FOR A CALUTRON HAVING AN OIL RESERVOIR IN ITS COLLECTION POCKET Filed May 9, 1966 3 Sheets-Sheet l INVENTORS. William A.Bell, Jr.

BY Allen M. Veach ATTORNEY.

April 1967 w A BELL, JR., ETAL 3,312,849

ISOTOPE RECEIVER FOR A CALUTRON HAVING AN OIL RESERVOIR IN ITS COLLECTION POCKET Filed May 9, 1966 3 Sheets-Sheet 2 INVENTORS. William A. Bell, Jr.

BY Alleh M. Veach ATTORNEY.

Ap il 1967 r w. A. BELL. JR. ETAL 3,

ISOTOPE RECEIVER FOR A CALUTRON HAVING AN OIL RESERVOIR IN ITS COLLECTION POCKET Filed May 9, 1966 5 Sheets-Sheet 3 INVENTORS. William A. Bell, Jr.

BY Allen M. VeqCh ATTORNEY.

. the course of, a contract with the United States Patent 3,312,849 ISOTOPE RECEIVER FOR A CALUTRON HAV- ING AN OIL RESERVOIR IN ITS COLLECTION POCKET William A. Bell, Jr., and Allen M. Veach, both of Oak Ridge, Tenn., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed May 9, 1966, Ser. No. 548,805 Claims. (Cl. 31363) The invention described herein was made under, or in U.S. Atomic Energy Commission.

This invention relates to an improved calutron isotope receiver in an isotope separating apparatus, whereby higher purity collection of low abundance isotopes, and/ or isotopes of elements of high vapor pressure can be achieved.

In a calutron, as is now well known, a beam of positive ions of the element to be separated is formed and ions of identical mass are projected at a uniform velocity into an evacuated region traversed by a substantially uniform magnetic field, the ions being projected at right angles to the direction of the field. As a result, each particular ion is caused to describe an arcuate path having a radius proportional to the square root of its mass. In this way, the original single ion beam is divided into two or more fairly discrete component beams, each of which consists primarily of individual isotopes of the material. Because of a geometrical and magnetic focusing action, the various beams are most distinctly resolved after the completionof 180 degrees of their arcuate path; the various isotopes, that is, the beams, diverge from each other dependently on their separate masses, and the beams may be individually collected in a receiver located at the focal point.

It is desired, of course, that the collected isotopes be as free as possible from contamination by adjacent beams or foreign material and it has long been an objective in the art to contrive a receiver capable of achieving increased production and purity without increased contamination. The projected purity of isotopes collected in a typical calutron operation is determined by noting the height of the peaks of specific ion currents and contrasting these with the valleys between the peaks. The product appears to be contaminated with varying amounts of material having about a natural abundance of the isotopes. Many possible explanations for this dilution of the enriched isotopes have been considered. For example, any variation in magnetic field or accelerating voltage will alter the focal position of the isotopic beam relative to the fixed collector and introduce contaminating masses. Likewise, gas scattering, charge exchange, beam oscillations, and migrating of neutrals (charge vapor) contribute to the contaminating process. However, little solution to the dilution problem has been accomplished prior to the present invention. It is known that the problem is increased when elements, or their compounds, having a high vapor pressure are being processed. Furthermore, it should be obvious that even a small dilution of a relatively low abundance isotope is a significant detriment in the purity of the collected isotope.

Thus, there exists a need for an improved isotope receiver in a calutron system in which an increase in production and purity can be achieved without an increase in contamination.

With a knowledge of the contamination problem in prior calutron systems and particularly with the use of high vapor pressure elements and/or compounds in such systems, it is the object of the present invention to provide an improved calutron receiver constructed in such a manner that a substantial increase in isotopic purity as 3,3 12,849 Patented Apr. 4, 1967 ICC well as an increase in production can be achieved while at the same time reducing the dilution problem.

This and other objects and advantages of the present invention will become apparent upon a consideration of the following detailed specification and the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a calutron receiver which the above object can be achieved;

FIG. 2 is a cross-sectional view of the recessed pocket of FIG. 1 showing the use of oil therein for the purpose to be described below;

FIG. 3 is a modification of the pocket of FIG. 2 which may be used in the device of FIG. 1;

FIG. 4 is another modification of the pocket of FIG. 2 which may be used in the device of FIG. 1; and

FIG. 5, FIG. 6, FIG. 7, and FIG. 8 are sectional views of conventional calutron receiver pockets utilizing the benefits of oil therein as to be described below.

The above object has been accomplished in the present invention by providing a cooled collection pocket positioned well behind the defining face plate of the receiver and providing cooled bafiles between the face plate and the recessed pocket for stopping high-energy neutrals and low-energy ions such that many ions having extraneous energy were diverted from the collection surface of the recessed pocket and the number of condensable neutrals reaching the collection surface of the recessed pocket was reduced by a factor approaching the inverse ratio of the area of the collection surface to the total area within the receiver. A further improvement in the purity of the collected isotope in the recessed pocket of the receiver has been accomplished by the use of oil placed in an oil reservoir in the recessed pocket, with the oil positioned so that a small portion of the ion beam strikes the oil in the reservoir. The advantages of such an arrangement will be discussed fully below. The use of oil in a receiver pocket of a calutron is not limited for use in the recessed pocket of the present invention, but has also been found to improve the operation of calutrons using conventional receiver pockets.

Referring now to the drawings, one improved isotope receiver of the present invention is shown in FIG. 1. The receiver of FIG. 1 may be used in a calutron system such as disclosed in the E. 0. Lawrence patent, No. 2,709,222. The receiver of FIG. 1 includes at least one conventional receiver pocket 1 with an access thereto through an entrance slit 2 in a face plate 3. The pocket 1 is defined by a housing 20 which is cooled by cooling tubes 11. The face plate 3 with plate members 15, 7, and 12 form a front housing of the receiver unit. The plate member 12, a back plate member 5, and the member 7 form a back housing of the receiver unit which is cooled by cooling tubes 8. A receiver pocket 6 is mounted adjacent to the back plate member 5 of the back housing. The pocket 6 is defined by a housing 18 which is cooled by cooling tubes 9, and the housing 18 may be provided with an isotope collection member 19 when such is required. The front housing, mentioned above, is provided with diverging plate members 13 and 14 in alignment with an ion entrance slit 16 in the face plate 3. The members 13 and 14 are cooled with cooling tubes 10- The ion beam 4, which represents one of the isotopes to be collected by the receiver, is not collected by a pocket adjacent to the face plate 3 as was done in conventional receivers of the prior art, but is directed through the channel provided by the water cooled plate members 13 and 14,'through an opening in plate member 12 and then through the back housing into the recessed pocket 6 where the desired isotope, represented by the ion beam 4, is collected on the collector 19.

Interposted between the plate member 12 of the back housing and the recessed pocket 6 are a plurality of upper baffles 23 supported by the member 7, and a baffle 25 supported by a bracket 24 to one of the battles 23, and

4 of FIG. 1 and those obtained with prior receivers is shown in the following table.

Subject Receiver Standard Prior Receiver Improve- Isotope ment in Natural Receiver Mass Enhance Mass Enhance- Ehhanec- Abundance Usage (hrs) Abundance ment Abdundance ment ment Factor (Percent) (Percent) Factor (12) (Percent) Factor (71) I'Ig19(i 0. 6,800 26.0 234 8. 3 60 3. 9O (la-46... 0. 0038 550 63. 5 52, 600 49. 4 29, 500 1. 78 S-33 0. 74 265 82. 9 650 71. 2 330 1. 97 (De-136.... 0. 193 100 75. 9 1, 620 29. 9 220 7. 36 Ce-l38 0. 125 64. 7 730 21. 2 105 6. 95 file-123.... 0. 87 675 85. 9 690 83. 3 570 1. 21

*n= where 0,, and C r are mass concentrations in percent in product and feed, respectively.

100C 100-Or a plurality of lower baffles 21 supported by the plate member 12. The bafiles 23 and 25 are water cooled by means of cooling tubes 26 and the bafties 21 are water cooled by means of cooling tubes 22. The upper bafiles 23 and 25 are used for trapping high-energy neutral particles and the lower bafiiles 21 are used for trapping lowenergy ions such that this arrangement of cooled bailies plus cooling the housing 7 is an effective means for substantially reducing either neutral or ionic contaminants which might also enter the collector pocket 6.

The receiver unit of FIG. 1 may be moved longitudinally or rotated, if desired, to provide the optimum position for the unit with respect to the incoming ion beams. This is accomplished by affixedly mounting the receiver unit to a shaft 29 which may be moved longitudinally or rotated by means, not shown, in a conventional manner. Shaft 2? is slidably and rotatably mounted within an opening in a stationary support member 17 by means of a nylon bearing and tube support member 28, a clamping flange 27, a clamping nut member 31, a vacuum seal and pump-out member 34 mounted within a hollowedout portion of nut 31, and a threaded plug 32 for holding the seal member 34 within the member 31. An O-ring seal member 33 is provided between the member 17 and the nut member 31.

A rotatable member 311 is also supported by the stationary support member 17 and this member is connected to a sliding shutter member in a conventional man ner, not shown, such that by rotating the member 36 the shutter may be positioned over the ion entrance slits in the face plate 3 of the receiver unit during start-up in the operation of the calutron, if such is desired.

Thus, the provision of the recessed pocket 6, the baffles and cooling means, as in the device of FIG. 1, described above, of the present invention provides for collecting an isotope where added purity can be achieved and especially with low abundance, high vapor pressure elements and/ or compounds. The placement of the recessed pocket 6 well back of the face plate 3 of the receiver and the use of water cooling for the baffles 23, 25, and 21, for the pocket 6 and for the back chamber of the receiver, has proven its superiority in high-purity collections of Ca, S, Ce, cc, Te, and Hg. In the case of Hg, a silver plate at the point of impingement of the ion beam permits sputtering of the Ag so as to overlay and amalgamate with any deposited Hg.

In the operation of the receiver of FIG. 1 in a calutron, many ions having extraneous energy are magnetically diverted from the collection surface 19 of the pocket 6 and are collected on the bafiies 21, and the number of condensable neutrals reaching the collection surface 19 is reduced by a factor approaching the inverse ratio of the area of the collection surface to the total area within the receiver. Many of these neutrals are collected on the baffies 23 and 25. A comparison of the results obtain in collecting the above-mentioned isotopes with the receiver The percentages given in the above table for mass abundance are the maximum isotopic purities achieved. The average purity achieved for each of the above isotopes is, of course, lower than the values given above. However, it should be evident from the above comparisons that a substantial improvement has been achieved in the enhancement factor using the present receiver as compared to a standard prior receiver.

It should be noted that the calutron system using the receiver of FIG. 1 of the present invention also includes a calcium vapor generator for increasing ion output in a manner as disclosed in the copending application of W. A. Bell, Jr., et al., Ser. No. 461,586, filed June 4, 1965. In that application a calcium boiler was provided Within the tank unit of a calutron and positioned in such a manner that the calcium vapor from the boiler was directed toward the ion beam from the ion source unit of the calutron such that the vapor sees the greatest portion of the ion beam from the ion source. The gettering action of the calcium helps to further reduce the tank pressure of the calutron. The use of such a calcium boiler increased the ion output by a factor of from 3 to 10, depending upon the isotope being collected. In addition, it was possible to increase the ion output for some of the mercury isotopes by a factor of 10 at about the same pocket purity while at the same time using no refrigeration of the liner by alcohol and/ or Dry Ice.

The Ca isotope, which should be low in Ca assay, is desired for medical research. The maximum purity of Ca achieved in the standard prior receiver was about 49.4% as shown in the above table and the product contained about 45% Ca. When the Ca ion beam was permitted to continue into the collector pocket 6 of FIG. 1, a product was obtained which assayed 63.5% Ca and only 2.6% Ca.

A product enriched in I-Ig is also desirable for medical research. The best previous material separated in a standard calutron was 8.3%, while the average assay was about 4.5%. These results were obtained at an average ion current of 1.52.0 ma. and with Dry Ice-alcohol refrigeration of the units. With the device of FIG. 1, described above, and using a calcium vapor generator, the product assayed 26.0% Hg, 11.2% l-Ig, 13.3% Hg, 17.5% Hg, 9.1% Hg, 20.5% Hg, and 2.4% Hg.

While the use of the calcium vapor generator increased the ion output and the use of the recessed pocket 6 in the receiver of FIG. 1. increased the purity over that achieved with prior receivers, the receiver still lacked an ideal arrangement for Hg collection; namely a permanent isotope collection surface that would retain energetic ions and yet reject neutrals having thermal energy. As mentioned above, samples of Hg are needed as starting material from which to produce radioactive Hg for use in medical research. Past samples of Hg were not ideally suited to this specific need since their Hg content was too high. The present invention encompasses a further modification to the receiver of FIG. 1 wherein even higher purities of the collected isotopes can be achieved and especially with Hg. Such a modification is shown in FIG. 2, wherein the pocket 6 of FIG. 1 is provided with a source of low vapor pressure oil 35 (e.g., Octoil-S) in the bottom of the pocket such that a small portion 2%) of the ion beam 4 strikes the oil 35. The energy of the impinging ions plus thevapor pressure characteristics of the oil cause transport of oil vapor from the reservoir to the ion collecting surface of member 19. This surface, being Water cooled, condenses the oil vapor in a thin and reasonably uniform film. The ion beam 4, composed of 35 kev. ions, strikes this oil film and a carbonaceous layer results from the cracking of the oil. During operation there exists a continuous oil-volatilization, film-condensation, and oil-carbonization process. Energetic ions are trapped in the continuously thickening carbonaceous layer while the oil covering the layer prevents the condensation and entrapment of neutral vapors by the isotope collecting surface. Removal of the iso topic material from the carbonized mass is accomplished simply by washing the carbonized layer off the substrate with an organic solvent (e.g., xylene), collecting the solids on paper filter, and subjecting the residue to vacuum distillation at 250-300 C. In the use of the pocket of FIG. 2 in the receiver of FIG. 1, much less than 1% of the isotope was found to have penetrated the oily layer and entered the metallic substrate. Consequently, ion sputtering of the metal plate or pocket used to support the oil film is virtually eliminated.

The collection pockets shown in FIG. 3 and FIG. 4 have also been used in the receiver of FIG. 1 as replacements for the pocket 6. In FIG. 3, a housing 36 contains an isotope collection surface 37, and a source of oil 39, and the housing 36 is cooled by water tubes 38. The ion beam 40 strikes a small portion of the oil 39 to effect the same operation as described for FIG. 2 above. In FIG. 4, a housing 41 contains an isotope collection surface 43 and a source of oil 45, and housing 41 is cooled by water tubes 42. The ion beam 44 strikes a small portion of the oil 45 to effect the same operation as described for FIG. 2 above.

Each of the pockets of FIGS. 2, 3, and 4 yielded substantial improvement in Hg purity due to rejection of thermal (neutral) mercury vapor by the collecting surface and when used in the receiver of FIG. 1 yielded maximum increases in Hg purity due to the action of this receiver which partially diverts from the collecting surface both energetic neutrals and ions having extraneous energy, as explained above.

Using oil in the pocket 6 of FIG. 1 in the operation of the calutron, the isotopic purity of Hg has increased markedly from the 48% range of standard prior receivers to an average of 44.7% and a maximum of 75.8%, and the rate of collection of contained Hg per tank-hour has increased by a factor of six due largely to the use of calcium-vapor pumping as described above. Thus, it can be seen that the maximum level of purity of Hg attained with the device of FIG. 1 without the use of the oil was 26%, and an improvement in the enhancement factor of 3.90, as can be seen from the table above. On the other hand, with the use of oil in the receiver pocket 6 of FIG. 1, the maximum purity achieved for Hg of 75.8% results in an improvement in the enhancement factor of 34.6.

It should be noted that the successful application of the continuous-layer collection technique for Hg requires a reasonable balance between ion current and the quantity of oil vaporized from the reservoir. Either inadequate or excessive amounts of oil relative to an optimum value lower the isotopic retention achieved.

The use of oil in a calutron receiver is not limited for use in the receiver of FIG. 1, as described above. It has been used in other receiver pockets such as shown in FIGS. 5, 6, 7, and 8, and can be used in most types of conventional pockets if such is desired. When oil is used in such pockets, the isotopic purity of the desired isotope is about above that achieved without the use of oil in the pockets. Of course, the use of oil in the recessed pocket 6 of FIG. 1 is preferred over the use of oil in conventional pockets for collecting low abundance, high vapor pressure isotopes due to the substantial improvement in the purity achieved thereby.

FIG. 5 shows a two-stage pocket of a conventional receiver and includes a face plate provided with an ion entrance slit 51 for receiving an ion beam 52. Mounted back of the plate 3 is a housing 49 enclosing a member 53, and an ion collector 54 with a central opening 55 therein. A source of oil 57 is placed in the housing 49 as shown. Mounted back of housing 49 is a housing 46 enclosing an ion collector 47 and a source of oil 56. Part of the ion beam 52 passes through opening '55 into the housing 46. Both housings are cooled by water cooling tubes such as tube 48, for example.

In FIG. 6, the receiver pocket shown includes a housing 58 joined to a housing 59 with an ion opening 61 therebetween. Housing 59 encloses an ion collector, not shown, and a source of oil 62 and the housing is cooled by a Water tube 63. The ion beam 60 enters the housing 5 8 and part thereof passes through opening 61 and strikes the oil 62 in housing 59.

In FIG. 7, the receiver pocket shown includes a housing 68 cooled by a water tube 69, plates 64 and 65 defining an ion entrance slit 67, and a source of oil 66.

In FIG. 8, the pocket shown includes a housing 72 cooled by a water cooling tube 76, an oil reservoir for containing a source of oil 71, and plates 73 and 75 defining an ion entrance slit 74.

The pocket 1 of FIG. 1, which is a conventional pocket, may also be provided with an oil reservoir, if such is desired. The pocket 6 of the receiver of FIG. 1 is not limited for use in collecting the isotopes listed in the above table, but can be used to increase the purity of other isotopes. For example, such other isotopes include Sr, Ta, S, K, V, 0, Fe, and Zn. Furthermore, if there is suflicient mass separation, more than one beam can be collected in the same manner.

In summary, the provision of the Water cooled recessed pocket 6 the provision of the water cooled baffles 23, 25, and 21, and the provision of oil in the pocket-6 of the receiver of FIG. 1 permits the collection of the mercury isotope Hg at purities which were heretofore impossible to attain. The use of the cooled baffles partially alleviates the mercury neutral-vapor problem, which effects more contamination than does any other isotopic separation performed; the use of oil in the recessed pocket 6 sub stantially eliminates the condensation and entrapment of the mercury neutral vapors by the isotope-collecting surface; and the use of the calcium-vapor getter-pump feature provides a substantial increase in the collection rate, such that Hg can he collected in an unrefrigerated system in milligram quantities per day and at previously uncontemplated levels of isotopic purity. Thus, the ability of the ab0ve-described calutron system to operate efficiently without liner refrigeration, particularly in the collection of the Hg isotope, will effect a saving of the order of hundreds of dollars per week in the operating costs of the system.

This invention has been described by -way of illustration rather than by way of limitation and it should be apparent that the present invention is equally applicable in fields other than those described.

What is claimed is:

1. In a calutron system including an ion source; an ion receiver provided with a) defining face plate with ion entrance slots therein, first ion collection pockets mounted back of said slots and a housing enclosing said pockets; an evacuated tank enclosing said ion source and receiver; means for providing a magnetic field for said calutron; and a calcium-vapor generator disposed within said tank I for directing a calcium vapor into the path of the ion beam from said ion source; the improvement comprising an enlarged second housing positioned back of said first housing, said housings having a common wall therebetween with said common wall being provided with an opening for passage of an isotope ion beam t-herethrough; a second ion collection pocket provided with an ion collection surface and mounted in a recessed position close to the back wall of said second housing and a substantial distance behind said first ion collection pocket; an additional ion entrance slot being provided in said face plate in alignment with said opening in said common wall such that the isotope beam of which added purity is desired passes through said additional ion entrance slot, through said opening in said common wall and then into said recessed pocket; a pair of water-cooled diverging plate members mounted within said first housing to define a channel through which said isotope ion beam can pass; a first plurality of baffies mounted within said second housing above the path of said isotope ion beam and in close proximity thereto for trapping high-energy neutral particles; a second plurality of baffies mounted Within said second housing below the path of said isotope ion beam and in close proximity thereto for trapping ions with extraneous energy; and means for respectively water cooling said second housing, all of said batlles and said recessed collection pocket, whereby the provision of said cooled recessed pocket, said cooled bafiies and housing, and said cooled diverging beam channeling members effects collection of a desired isotope with substantially improved purity.

2. The calutron system set forth in claim 1, wherein said recessed second ion collection pocket is provided With a reservoir in the bottom portion thereof, and a source of oil being placed in said reservoir and having such a level that only a small portion of said isotope ion beam strikes said oil to etfect transport of oil vapor to the cooled ion collecting surface of said recessed pocket.

3. The calutron system set forth in claim 1, wherein said ion-collecting pockets in said first housing are provided with a source of oil in the lower portion thereof.

4. The calutron system set forth in claim 2, wherein said ion-collecting pockets in said first housing are provided with a source of oil in the lower portion thereof.

5. The calutron system set forth in claim 1, wherein the said recessed pocket is adapted to collect an isotope selected from the group comprising Hg, Ca, 8, Ce, 133c 123T 16 e 180T 36S 40 5812C, and 'zo References Cited by the Applicant UNlTED STATES PATENTS 2,906,876 9/1959 Brunk.

JAMES W. LAWRENCE, Primary Examiner.

S. D. SCHLOSSER, Assistant Examiner. 

1. IN A CALUTRON SYSTEM INCLUDING AN ION SOURCE; AN ION RECEIVER PROVIDED WITH A DEFINING FACE PLATE WITH ION ENTRANCE SLOTS THEREIN, FIRST ION COLLECTION POCKETS MOUNTED BACK OF SAID SLOTS AND A HOUSING ENCLOSING SAID POCKETS; AN EVACUATED TANK ENCLOSING SAID ION SOURCE AND RECEIVER; MEANS FOR PROVIDING A MAGENTIC FIELD FOR SAID CALUTRON; AND A CALCIUM-VAPOR GENERATOR DISPOSED WITHIN SAID TANK FOR DIRECTING A CALCIUM VAPOR INTO THE PATH OF THE ION BEAM FROM SAID ION SOURCE; THE IMPROVEMENT COMPRISING AN ENLARGED SECOND HOUSING POSITIONED BACK OF SAID FIRST HOUSING, SAID HOUSING HAVING A COMMON WALL THEREBETWEEN WITH SAID COMMON WALL BEING PROVIDED WITH AN OPENING FOR PASSAGE OF AN ISOTOPE ION BEAM THERETHROUGH; A SECOND ION COLLECTION POCKET PROVIDED WITH AN ION COLLECTION SURFACE AND MOUNTED IN A RECESSED POSITION CLOSE TO THE BACK WALL OF SAID SECOND HOUSING AND A SUBSTANTIAL DISTANCE BEHIND SAID FIRST ION COLLECTION POCKET; AN ADDITIONAL ION ENTRANCE SLOT BEING PROVIDED IN SAID FACE PLATE IN ALIGNMENT WITH SAID OPENING IN SAID COMMON WALL SUCH THAT THE ISOTOPE BEAM OF WHICH ADDED PURITY IS 